1. Field of the Invention
The present invention relates to an image forming apparatus in which a plurality of images are superposed on an image receiving member conveyed on a conveyor belt through a plurality of image forming stations.
2. Description of the Related Art
The Japanese Patent publication (Kokai) No. 3-181979 discloses a means to adhere the sheet-like transfer medium to the conveyor belt in an image forming apparatus. According to this means, a conductive roller is provided in contact with the transfer medium and a power supply applies a bias voltage to the conductive roller. The transfer medium is supplied with an electrical charge and therefore is adhered on the conveyor belt electrostatically. The adhered transfer medium is transferred forward to an image forming station, where an image formed on an image carrier is transferred onto the transfer medium.
However, this method has a problem that the transfer medium could not be sufficiently adhered when an electrical resistance of the transfer medium had dropped during a highly humidity condition. To solve this problem, it can be considered to increase the bias voltage to be applied to the conductive roller, but in this case there is also such a problem that a power supply of high voltage is required and an increase of size/manufacturing cost of the apparatus may result.
The transfer medium moves on the conveyor belt if not fully adhered, therefore it is difficult to form a color image which is formed by the passage of the transfer medium through a plurality of image forming stations, as misregistration among the images on the transfer medium occurs.